The invention relates to a semiconductor photodetector. Photodetectors are generally supposed to be as sensitive as possible and useful over a wide dynamic range of incident light intensity. In order to obtain a signal that can be evaluated, even at low light intensity, photosensitive elements are frequently followed by an amplifier arrangement which has a nonlinear amplifier characteristic to accommodate the wide dynamic range.
Photodetectors having internal amplification, for example, in the form of avalanche diodes or phototransistors, are already known.
Avalanche photodiodes for a wide wavelength range are described in, for example, D. Law et al, "Alloy Heterostructure High Speed Avalanche Photodiodes", Journal of Quantum Electronics, QE15, 549 (1979). Bipolar, or heterobipolar, phototransistors are described in, for example, S. Chandrasekhar et al: "High Speed Monolithic P-I-N/HBT and HPT/HBT Photoreceivers Implemented With Simple Phototransistor Structures", Proc. ECOC Conference 1993, Berlin, Germany. These solutions, however, have numerous drawbacks. Avalanche diodes are very sensitive, but require additional electronic measures to increase the dynamics. In contrast, the bipolar phototransistors are insensitive at low light intensity. The sensitivities of the two detector types are typically in a range between 10 A/W and 1000 A/W.
A field effect transistor arrangement used as a photodetector is known from U.S. Pat. No. 3,366,802. In this arrangement an n-doped zone is built into a p-doped substrate. In this n-doped zone more heavily n-doped source and drain contact regions are again realized. In addition, a gate region can be provided between the source contact and the drain contact. The p-n junctions form space-charge regions that constrict the source-drain connection. During light incidence, the width of the space-charge regions is reduced, and the conductivity of the component is thereby increased.
In U.S. Pat. No. 4,326,210.A, a photosensitive field effect component is described which has a slightly conductive layer on the surface, with at least two gate regions and a source contact surrounded by the gate regions, with which contact a drain contact on the opposite substrate side is associated. A current channel extending perpendicularly to the component surface is pinched off by space-charge regions that form regions at the p-n junctions of the gate. During light incidence, the space-charge regions are reduced, and a current flowing between source and drain is emitted as an electrical signal.